2016 Emerald Ash Borer Update

It’s been about a year since the first confirmed appearance of the emerald ash borer (EAB) in Lancaster County (Mount Joy Township, May 8, 2015).

Are you seeing much EAB infestation locally?
Some. At this point, it’s much more prevalent in Dauphin County. We have seen it in isolated locations in Lancaster County, but it’s not widespread yet.

I recently visited a wooded lot in Dauphin County for a client. My recommendation was removal. The infected trees aren’t worth saving, and there are no trees by the house we can save.

The only place in Lancaster County that we have conclusively identified EAB ourselves was at a tree removal in Lititz. The tree was already declining and when we removed it for a client, the tops showed evidence of EAB.

How quickly will EAB infest Lancaster County?
I think the populations are going to explode really quickly. Here’s how it will go down: to the untrained eye, one day everything is fine and next day the trees are just riddled.

To the trained eye, the early signs are beginning to crop up. The population starts feeding in the treetops because that’s where they fly. As they feed and propagate, they lay eggs on the bark, and the larvae do damage underneath the bark. As the population increases, they move their way down the tree. When you see evidence of EAB at the bottom of the tree, that’s where you know the populations are heavy.

D-shaped EAB emergence hole

How does one spot an EAB-infested tree?
One of the things I look for is areas of bark that have turned gray (see photo). The other, more obvious clue is the D-shaped emergence hole. When the insect goes from the larval stage to the adult stage, it chews its way out, and the hole is always D-shaped. Sometimes you have to pull away loose bark to see it. Obviously, if you are at ground level and seeing this, the tree is heavily infested.

Has your treatment to protect ash trees against EAB changed?
Yes, now that there is active infestation in the area, we inject directly into the trunk rather than into the soil at the base of the tree. This greatly speeds up the process of circulating the pesticide throughout the tree.

What is the mortality rate for ash trees in the path of EAB?
One hundred percent. EAB is on its way and it’s not going to disappear. Widespread tree death and damage are inevitable. Deciding to wait it out is not an option, although many people are still thinking that way in the early stages.

Unfortunately, EAB has no natural predators in North America, so there is nothing to stop it.

Can natural predators be imported to stop EAB?
There is a wasp out there that has been released with limited success. The difficulty with that is, predators need something to eat. So you can’t introduce them BEFORE the pest arrives. Further, predacious insects manage the population, they don’t wipe it out… otherwise they’d starve. So they’re not a total solution.

What will the ash tree population look like in the future?
A historical example is Dutch elm disease in the 1960s and 1970s. Most Dutch elm trees are gone, and those still alive in urban areas are being treated with chemicals to protect them.

Look at American chestnuts, which were wiped out by a fungal disease called chestnut blight. They still stump sprout, but the small shoots get the disease. There are a few hundred mature specimens still growing in Michigan.

With EAB, it helps to think of the infestation as a wave. The first wave is the biggest, and will wipe out most unprotected trees. Afterward, the insect population will diminish quite a bit but won’t vanish.

We’re already seeing how this works in Michigan… we’re seeing re-infestation. People get complacent and don’t treat– or stop treating– their ash trees. Then another wave comes along and wipes them out. Then a third wave.

We publish a quarterly newsletter that's full of helpful information and tips on caring for your trees and lawn, names of our drawing winners, and updates on what’s happening with us. Click here to view the Arborist Almanac Newsletter.